Light collection and detection apparatus comprising plural light sensors so spaced that the composite response is independent of source position

ABSTRACT

Disclosed is light collection and detection apparatus which exhibits a substantially uniform response characteristic with respect to a diffuse spot of light which may emanate from any point on a planar source such as exists where a flying spot scanner scans a photographic transparency that is positioned on a translucent, opal glass plate. Located below the glass plate and separated therefrom by a chosen distance is a plurality of photomultipliers, each having a known polar light response characteristic which is nonuniform with respect to at least some of the possible points from which the diffuse spot of light may emanate on the opal surface of the glass plate. Each of the photomultipliers develops an output signal representative of the intensity of the diffuse spot, and the plurality of photomultipliers are arranged in a predetermined array in a plane substantially parallel to that of the glass plate so as to effect an overlapping of the light response characteristics of the individual photomultipliers by a selected amount in the plane of the opal glass plate. The output signals from the individual photomultipliers are additively combined to develop a resultant output signal whose amplitude is substantially linearly proportional to the intensity of the diffuse spot of light regardless of the location of the point on the opal glass plate from which the spot of light emanates. Other embodiments are disclosed.

United States Patent Charles E. Page Westbury;

Gustavo A. Andersen, Hollis, both of N.Y. [21] Appl. No. 874,548

[72] Inventors [22] Filed Nov. 6, 1969 [45] Patented Nov. 2, 1971Hazeltine Corporation [73] Assignee [54] LIGHT COLLECTION AND DETECTIONAPPARATUS COMPRISING PLURAL LIGHT SENSORS SO SPACED THAT THE COMPOSITERESPONSE IS INDEPENDENT OF SOURCE Primary Examiner-James W. LawrenceAssistant Examiner-T. N. Grigsby Anorney- Kenneth P. Robinson ABSTRACT:Disclosed is light collection and detection apparatus which exhibits asubstantially uniform response characteristic with respect to a diffusespot of light which may emanate from any point on a planar source suchas exists where a flying spot scanner scans a photographic transparencythat is positioned on a translucent, opal glass plate. Located below theglass plate and separated therefrom by a chosen distance is a pluralityof photomultipliers, each having a known polar light responsecharacteristic which is nonuniform with respect to at least some ofthepossible points from which the diffuse spot of light may emanate on theopal surface of the glass plate. Each of the photomultipliers developsan output signal representative of the intensity of the diffuse spot,and the plurality of photomultipliers are arranged in a predeterminedarray in a plane substantially parallel to that of the glass plate so asto effect an overlapping of the light response characteristics of theindividual photomultipliers by a selected amount in the plane ofthe opalglass plate. The out-v put signals from the individual photomultipliersare additively combined to develop a resultant output signal whoseamplitude is substantially linearly proportional to the intensity of thediffuse spot of light regardless of the location of the point on theopal glass plate from which the spot of light emanates. Otherembodiments are disclosed.

OUTPUT PATENTEnuu'v 2 Ian SHEET 2 0F 2 LIGHT COLLECTION AND DETECTIONAPPARATUS COMPRISING PLURAL LIGHT SENSORS SO SPACED THAT THE COMPOSITERESPONSE IS INDEPENDENT OF SOURCE POSITION The present invention relatesto light collection and detection apparatus, and more particularly tosuch apparatus which is capable of responding uniformly to a spot oflight which may emanate from any point on a planar source.

There exist in the art systems, such as those used to analyzephotographic transparencies, wherein it is desirable to uniformlycollect and detect light which may emanate from any point on a large,usually planar surface, such as the transparency. In the case ofphotographic transparency analysis, the transparency is normally scannedin a TV raster format with a small spot of light from a flying spotscanner. The resulting light transmitted by the transparency is thencollected and detected to develop a video signal whose instantaneousamplitude is proportional to the transmissivity of successively scannedelemental areas of the transparency. If the transparency is of anyconsiderable size, such as 5, or even inches in length, it is verydifficult'to design a practical light collection and detection systemwhich is uniformly responsive to the light transmitted by each elementalarea of the transparency, regardless of whether the element is at thecenter or at one of the corners of the transparency. The conventionalapproach is to utilize a large collection lens to focus lighttransmitted by the transparency onto a single light detector, such as aphotomultiplier. A system of this type has inherent limitations anddisadvantages resulting from its size, such as the necessarily high costof such a large lens and the nonuniform light characteristics of such alens-light detector combination. It would, therefore, be highlydesirable to have for use in systems such as that just described, arelatively simple and inexpensive light collection and detectionarrangement which exhibits a substantially uniform responsecharacteristic over the entire transparency area, regardless of the sizeof that area.

1 It is therefore an object of the present invention to provide new andimproved light collection and detection apparatus which is not onlyexhibits a substantially uniform response characteristic for lightemanating from any point on a, planar source, but also is of relativelysimple and inexpensive construction.

It is a further object of the presentjnvention to provide new andimproved light collection and detection apparatus which utilizes anarray of individual light detection devices to synthesize a single lightdetection device having a uniform response characteristic for lightemanating from any point on a planar source.

It is still another object of the invention to provide new and improvedlight collection and detection apparatus which utilizes novellight-reflecting structures'to minimize the number of light detectiondevices necessaryi'in such an array and to render even more uniform thelight response characteristic of the array.

In accordance with the present invention .there is provided lightcollection and detection apparatus which exhibits a sub-, stantiallyuniform response characteristic with respect to an intensity-modulateddiffuse spot of light which may emanate from any point on a planarsource which comprises a plurality of light detection means, each havinga known polar light response characteristic which is nonuniform withrespect to at least some of the possible points from which theintensitymodulated diffuse spot of light may-emanate on the source, eachof the detection means for developing an output signal representative ofthe intensity of the diffuse spot of light, the plurality of detectionmeans being arranged in a predetermined array to effect an overlappingof the individual light response characteristics by a selected amount inthe plane of the source. The apparatus further comprises means forcombining the output signals of the light detection means to develop aresultant output signal whose amplitude is substantially linearlyproportional to the intensity of the diffuse spot of light regardless ofthe location of the point on the source from which the spot oflightemanates.

For a better understanding of the present invention together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings and itsscope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of lightcollection and detection apparatus constructed in accordance with oneembodiment of the present invention;

FIG. 2 is a top plan view of a portion of the light collection anddetection apparatus of FIG. I;

FIGS. 3, 6 and 7 are plots of overlapping photomultiplier responsecharacteristics useful in describing the construction and operation ofthe apparatus of FIGS. 1 and 2; Y

FIG. 4 isa plot of the polar response characteristic for a typicalflat-faced photomultiplier, such as is used in the embodiment of FIG. 1,and

FIG. 5 is a plot of the composite response characteristic achieved bythe light collection and detection apparatus of FIG. I.

DESCRIPTION OF THE APPARATUS In FIGS. 1 and 2 of the drawings, there isshown in side and top plan views, respectively, one embodiment of lightcollection and detection apparatus constructed in accordance with thepresent invention. In describing the apparatus of FIGS.,I and 2, it isassumed that by means of a flying spot scanner l0 and an imaging lens11, a photographic transparency 12, located in the image plane of lens11, is scanned with a spot of light (typically 4 mils in diameter) in apoint-by-point, line-byline fashion that iswell known in the art. Inaccordance with one embodiment of the invention, a glass plate I3 havinga translucent white, opal surface is placed under the transparency 12with the opal surface adjacent thereto, such that at any instant of timeduring the scanning process, light from scanner 10 that is transmittedthrough transparency 12 is diffused by the opal surface of glass plate13 and appears as an intensity-modulated diffuse spot of lightwhich mayemanate from any point in the plane of the opal glass surface. Glassplate 13 comprises planar light-diffusing means, located adjacent andsubstantially parallel to the plane of transparency 12, for diffusingthe light which is transmitted by the transparency to provide anintensity-modulated diffuse spot of light which may emanate from anypoint on the planar source represented by the glass plate. 7

Located below plate 13 in FIG. I is that portion of the light collectionand detection apparatus shown in plan view in FIG. 2, which consists ofan array of four photomultipliers 15a, 15b, 15c and 15d, surrounded by afour-sided, bottomless, boxlike light reflecting structure I4 whoseinterior surfaces are highly reflective, and whose walls aresubstantially perpendicular to the plane of glass plate 13. Structure 14can be made from micropolished aluminum, for example, which has asurface reflectivity of approximately 75 percent. In the presentembodiment the array of photomultipliers l5a-l5d, arranged in two rowsand two ,columns, comprises a plurality of light detection means, eachhaving a known polar light response characteristic which is nonuniformwith respect to at least some of the possible points from which thediffuse spot of light may emanate onthe opal surface of glass plate 13.Each of the light detection means develops an output signal whoseamplitude is representative of the intensity of the diffuse spot oflight. The detection means are arranged in a predetermined array in aplane substantially parallel to that of the glass plate I3 and separatedtherefrom by a chosen distance, thereby to effect an overlapping of theindividual light response characteristic of the light detection means bya selected amount in the plane of the opal glass. Furthermore, in thepresent embodiment light reflective structure 14 comprises one form oflight-reflecting means, arranged adjacent to at least some of the lightdetection means in the array, for forming mirror images of at least someof the light detection means, thereby increasing the apparent number oflight detection means in the array whose individual polar light responsecharacteristics overlap in the plane of the opal surface of glass plate13.

While in the embodiment of FIG. 1, the lighbreflecting structure 14 isnot a necessity, its use significantly simplifies the apparatus, therebyreducing size and cost. If a lightreflecting means similar to structure14 is not utilized, it is then necessary to increase the number ofactual photomultipliers in the array by adding at least one additionalphotomultiplier at each end of each row and each column of existingphotomultipliers, as shown in FIG. 6, thereby requiring a total of atleast l2 photomultipliers to perform substantially the same functionachieved in the embodiment of FIG. 1 with only four photomultipliers andthe light-reflecting structure 14. Since structure 14 creates only anapproximation of a larger array of photomultipliers, 'and since thereflective material used to fabricate the boxlike structure is not aperfect reflector, it will be recognized that a higher degree of lightresponse uniformity can be achieved by using an actual larger array ofphotomultipliers. Thus, in its broadest sense, the present inventiondisclosed an array of light-detecting means, such as photomultipliers,utilized in a novel manner to achieve a desired degree of uniformresponse to a scanning, diffuse spot of light of variable intensitybccurring with a defined planar area. Moreover, in accordance withanother aspect of the invention, a novel technique is disclosed by whichthe number of light detectors in such an array can be reduced by the useof novel and inexpensive light-reflecting structures. Not only does thislatter aspect of the invention provide an effective means for reducingthe actual size and complexity of such an array, but also the resultingsmaller array still exhibits a substantially uniform light responsecharacteristic.

The apparatus of FIGS. 1 and 2 further includes means for combining theindividual output signals of the photomultipliers l5a-I5d to develop aresultant output signal whose amplitude is substantially linearlyproportional to the intensity of the diffuse spot of light from the opalsurface of glass plate 13, regardless of the location of the point onthe opal surface from which the diffuse spot of light emanates. In theembodiment of FIGS. 1 and 2, this combining means is shown as a simpleadder 16, which linearly adds the individual output signals developed bythe four photomultipliers to develop a single resultant output signal.In its simplest form, adder 16 may be a common conductor whichis jointlyconnected to the outputs ofall four photomultipliers.

It should be noted that the light collection and detection apparatus ofFIGS. 1 and 2 is particularly unique in that is does not employ any lensor lens systems whatsoever, but relies solely on the novel andunconventional use of simple light detectors such a photomultipliers,arranged in a selected array and responsive to a scanning, diffuse spotof light. The number, spacing and arrangement of photomultipliers usedin a particular embodiment are dependent on the size of the area coveredby the planar source from which it is desired to collect and detect thescanning diffuseflight, as will be described in detail hereinafter.While in the particular embodiment of FIGS. I and 2 fourphotomultipliersare shown, this number is not intended to limit in anyway the number of photomultipliers which may be used in accordance withthe present invention to achieve a desired degree of uniformity in thelight response characteristic.

CONSTRUCTION AND OPERATION OF THE APPARATUS In constructing lightcollection and detection apparatus in accordance with the presentinvention, it is first necessary to choose the type of photodetector tobe used, and to ascertain the polar light response characteristic forthat type detector. However, since photodetectors are conventionallyused in such a manner that the light to be detected is focused on theface of the detector, and in this mode of use its polar light responsecharacteristic is irrelevant, this response characteristic normally isnot specified by the manufacturer. Thus, it may be necessary toempirically determine the polar light response characteristic of thephotodetector chosen for use in apparatus of the present invention. Ifphotomultipliers are chosen as the type of light detectors to be used,it has been determined that presently available photomultipliers whichare of the flat-faced type, exhibit the same general form of polar lightresponse characteristic. One quadrant of this characteristic is shown inFIG. 4 of the drawings, and if revolved through 360 about the verticalaxis, it will provide the overall polar light response characteristicfor typical flatfaced-type photomultipliers.

Having determined the polar light response characteristic of the type ofphotodetector to be used, it is then possible to proceed with adetermination of the parameters of an array of such photodetectors whichwill provide the desired uniform response characteristics for lightemanating from any point on the planar source represented by the opalsurface of glass plate 13 in the apparatus of FIG. 1, for example.

A suitable array may consist of a plurality of photomultipliers arrangedin a pattern of perpendicular rows and columns, with the spacing betweenphotomultipliers in any row and any column being the same, and beingsuch that the polar light response characteristics of the individualphotomultipliers overlap one another to a desired degree in the plane ofthe light source (i.e.: the plane of the opal glass of plate 13). Thecenter-to-center spacing of photomultipliers in the array is related tothe shape of the'polar light response characteristic of an individualphotomultiplier and also to the distance between the plane of the opalglass and the plane of the photomultiplier array. It has been determinedthat this relationship is similar to that which is utilized in the fieldof illumination engineering to determine the parameters necessary for anarray of lighting fixtures which will provide substantially uniformillumination of a planar surface which is parallel to the fixture array.(See Light, Photometry, and Illuminating Engineering" by W.E. Barrows,pp. 222 et seq., McGraw-Hill 1951).) This relationship is given as:

K=d/h where:

([K]is a factor determined by the shape of the polar light responsecharacteristic of an individual photomultiplier (similar to the polarillumination characteristic of an individual lighting fixture);

[dlis the center-to-center spacing of the photomultipliers in the array(similar to the center-to-center spacing of lighting fixtures in theillumination array); and

[hlis the distance between the planar light source, represented by theopal glass of plate 13, and the photomul tiplier array (similar to thedistance between the surface to be illuminated and the array of lightingfixtures).

In the field of illumination engineering, the above relationship hasbeen reduced to a set of curves which show the polar illuminationcharacteristics necessary to give uniform illumination of a planarsurface at different values of K, the most common values being K=%,=%,l,l'/4 and 1% and 2 (see Standard Relations of Light Distribution" byAJ. Sweet, I. E. 8., Vol. 4, pg. 745 at pg.755, I909). By comparing thecharacteristic of FIG. 4 with the various curves of this set, it hasbeen determined that this polar light response characteristic for atypical flat-faced photomultiplier corresponds substantially to theillumination characteristic curve given for a K of 1%. With the factor Kthus determined for typical flatfaced photomultipliers, theproportionality between (d) and (h) is fixed, and these parameters maybe readily determined by specifying one and solving for the other. Forexample, in the present case where a K of 1% has been shown to beapplicable, it is possible to specify a convenient distance (h) betweenthe plane of the photomultiplier array and the opal surface of glassplate 13, and thereafter solve for the corresponding center-to-centerspacing (d) of the photomultipliers, or alternatively one can specify aconvenient centerto-center spacing (d) and solve for the correspondingdistance (h).

The remaining parameter to be determined is the number ofphotomultipliers necessary in the array. In the simplest case, where anarray of photomultipliers is used without any light reflectingstructures, this number is determined-by superimposing an array ofphotomultipliers spaced (d) units center-tocenter onto the planar source(in this case glass plate 13) from which light is to be collected anddetected. A circle-of radius (d) is then drawn about the center of eachphotomultiplier, intersecting the centers of adjacent photomultipliersas shown in FIG. 3. The array of photomultipliers is then increased innumber and/or its position relative tothe planar source shifted untilevery point on the planar source is covered. by at least two of theoverlapping circles as shown in FIG. 6, which circles representoverlapping of the polar light response charac teristics of theindividual photomultipliers. The number of photomultipliers required toprovide this selected amount-of overlap (i.e.: l2 in the FIG. 6 array)then is the least number necessary in a simple array whose overall lightresponse characteristic will be substantially luniform with respect'to adiffuse spot of light emanating from any point on the planar source(i.e.: the opal surface of glassplate 13).

As described previously, in accordance with another aspect of theinvention, novel light-reflecting structures can be employed in lightcollection and detection apparatus such as that just discussed in orderto reducethe number of photomultipliers required to provide a givendegree of uniform light responsiveness and to modify the existing lightresponse characteristic so as to make it even more uniform.Thesimplest'light reflecting structure isthat shown in FIG. 1 as thefour-sided box 14 having the same outside dimensions asthe glass plate13. The interior surfaces of box 14 have a reflectivity of 75 percent,which has been found to be sufficient togive satisfactory results. Thisreflectivity can be readily achieved with a simple, light weight boxconstructed of micropolished aluminum. Within box 14 the photomultiplierarray is positioned such that the center-to-center spacing of thephotomultipliers is (d) and the perpendicular distance between thecenters of the photomultipliers and the adjacent interiorsurfaces of box14 is (1/2, as shown in FIG.'2. With this arrangement, the reflectingwalls of box 14 servel'to create mirror images of the actualphotomultipliers in the array, with the mirror images appearing at thesame center-to-center spacing (d) as is the case in the actual array.These images appear to be located outside of the light-reflecting box14, as shown in FIG. 7, and therefore operate to extend the apparentsize of the array, without increasing its actual size. This can beseen-by comparing FIGS. 6 and 7. In FIG. the amount of overlapattributable to the light response characteristics of the actualphotomultipliers (shown as the solid arcs) and the light responsecharacteristics of the mirror image photomultipliers (shown as thedotted arcs) is substantially the same as that of FIG. 6 where thelarger number of actual photomultipliers is used. Thus, by utilizingsimple light reflecting structures in accordance with the invention, anygiven size array of photomultipliers can be made to function in a mannerequivalent tothat of a larger array. In this manner the cost ofadditional photomultipliers can be saved by introducing a simplelightreflecting structure such as box 14 shown in FIGS. 1 and 2.

In the embodiment of FIGS. 1 and 2 the uniformity of its light responseis established in an initial setup procedure, during which time notransparency is placed on glass plate 13 and the normal deflectioncircuitry of scanner is disabled. Adjustable DC voltages are supplied,instead to the deflection Coils of scanner 10 so that the position ofits light beam on the glass plate 13 can be manually controlled. Theresulting diffuse spot of light is then positioned directly over one ofthe photomultipliers 1511-1511 and bias voltages on thatphotomultiplier, which control its gain, are, adjusted until the desiredmaximum amplitude of output signal is obtained. Likewise, the spot oflight is successively positioned over each of the remaining threephotomultipliers and their respective gains adjusted until each developsthe aforementioned desired maximum amplitude output signal when the spotis directly over it. With the setup procedure thus completed the normaldeflection circuitry for the flying spot scanner is reactivated andtheapparatus will, thereafter function as described above, exhibiting atthe output of adder 16 the desired uniformity in its response to thediffuse spot of light emanating from any point on the opal surface ofglass plate13.

In accordance with still another aspect of the invention, a second typeof light-reflecting structure can be introduced within the array inorderto increase its overall uniformity by increasing the apparent number ofphotomultipliers in the array. This-second type of light-reflectingstructure is shown in FIGS. 1 and 2 as being the wedge-shaped units 17located, in this case, midway between each pair of photomultipliers, andcan be constructed of the same highly reflective material as box 14. Ifthe sides of each wedge-shaped unit 17 are set at an angle of 45, to thevertical, for example, eachunit will create mirror images of the pair ofactual photomultipliers located on each'side of the unit and adjacentthereto, with theseimages appearing between the pair ofphotomultipliers. Altering the slope of the sides of the wedge-shapedunit will correspondingly'alterthe apparent position of the mirrorimages. Thispermits adjustment of the position of the polar lightresponse characteristics of the mirror image photomultipliers, therebyvarying the amount by which these latter characteristics overlap'thelight response characteristics of the actual photomultipliers in thearray.

It has been found that the overall light response characteristics'forthe array of photomultipliers shown'in FIGS. 1 and 2 with the boxlikelight-reflecting structure 14, but without the wedge-shapedlight-reflecting structures 17, is of the form shown in FIG. 5 of thedrawings. While light collection and detection apparatus havinganoverall light response characteristic such as this is useful inmanyapplications, nevertheless it can be seen that this characteristicdoes exhibit a slight valley at its center, and asmall amountof falloffat its ends. Yet, in accordance with the further aspect of the inventionthis characteristic can be rendered even more uniform by simplyintroducing thewedge-shaped light reflectors 17, shown in FIGS. 1 and 2.The effect of adding these reflectors is to raise the central valley inthe response characteristic of FIG. 5 by creating photomultiplier mirrorimages near the location of this valley. The characteristic of FIG. 5can be made even more uniform by increasing slightly the separation (d)of,the' actual photomultipliers, while at the same time retaining thewedge-shaped light reflectors 17. Increasing the separation betweenphotomultipliers serves to raise the ends of the light responsecharacteristic of FIG. 5 by placing both the actual photomultipliers andthe mirror images thereof, created by the walls of box 14, nearer to theedges of the glass plate 13, from which light is being collected anddetected. While this increase in separation of the photomultipliers willalso increase the depth of the central valley inthe characteristicofFIG. 5, nevertheless, this valley can be raised sufficiently by meansof the wedge-shaped reflectors 17 so asto achieve an overall lightresponse characteristic which exhibits substantial uniformity over itsentire length.

The aforementioned technique of increasing the separation of thephotomultipliers can also be used to accommodate light sources which arerectangulanshaped instead of squareshaped as is the configuration shownin FIGS. 1 and 2. If for example the side-to-side width of theglassplate 13 in FIG. 1 were greater thanits front-to-back depth, thiscould easily be accommodated while still using the four photomultiplierarray of FIGS. 1 and 2 by simply increasing the center-to-center spacing(d iof the photomultiplier pairs *1 50-15 b and the pair l5c-l5d. Inthis case, the center-to-center spacing (11,) inFIG. 2 would be greaterthan and not equal to thecenter-to-center spacing ((1,). By using thewedge-shaped light reflectors 17 the deeper valley which would otherwisebe created by this separation in the light response characteristic ofFIG. 5 can be raised sufficiently to create an overall substantiallyuniform light response characteristic.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it

will be obvious to those skilled in the art that various changes andmodificatons may be made therein without departing from the inventionand it is, therefore, aimed to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. Light collection and detection apparatus which exhibits asubstantially uniform response characteristic with respect to anintensity-modulated diffuse spot of light which may emanate from anypoint on a planar source, comprising:

a plurality of light detection means, each having a known polar lightresponse characteristic which is nonuniform with respect to at leastsome of the possible points from which said intensity-modulated diffusespot of light may emanate on said source, each of said detection meansfor developing an output signal representative of the intensity of saiddiffuse spot of light, said plurality of detection means being arrangedin a predetermined array to effect an overlapping of said individuallight response characteristics by a selected amount in the plane of saidsource;

and means for combining the output signals of said light detection meansto develop a resultant output signal whose amplitude is substantiallylinearly proportional to the intensity of said diffuse spot of lightregardless of the location of the point on said source from which saidspot of light emanates.

2. Apparatus constructed in accordance with claim 1 wherein said lightdetection means are arranged in said predetermined array in a planesubstantially parallel to that of said source ans separated therefrom bya chosen distance, thereby to effect said selected amouht of overlappingof said light response characteristics.

3. Apparatus constructed in accordance with claim 1 wherein each of saidlight detection means is a photomultiplier and wherein said means forcombining the output signals of said photomultipliers is a conductorconnected to the output of each photomultiplier.

4. Apparatus constructed in accordance with claim 1 wherein saidapparatus additionally includes light-reflecting means, arrangedadjacent to at least some of the light-detection means in said array,for formingl mirror images of at least some of said light detectionmeans, thereby increasing the apparent number of light detection meansin said array whose individual polar light response characteristicsoverlap in the plane ofsaid source. I

5. Apparatus constructed in accordance with claim 4 wherein saidlight-reflecting means is a boxlike structure, having wallssubstantially perpendicular to the plane of said source and surroundingsaid array of light detection means, the interior surfaces of saidstructure being light-reflective to form said mirror images.

6. Apparatus constructed in accordance with claim 4 wherein saidlight-reflecting meanscomprises at least one wedge-shapedlight-reflecting structure located within said arrayand between at leasta pair of said light detection means for forming mirror images of saidpair of light detection means, the exterior surfaces of saidwedge-shaped structure being light reflective to form said mirrorimages.

7. Apparatus constructed in accordance with claim 1 wherein saidapparatus additionally ,includes a boxlike lightreflecting structure,having walls substantially perpendicular to the plane of said source andsurrounding said array of light detection means, for forming mirrorimages of at least some of said light detection means, therebyincreasing the apparent number of light detection means whose individualpolar light response characteristics overlap in the plane of saidsource, the interior surfaces of said boxlike structure beinglightreflective to form said mirror images;

and at least one wedge-shaped light reflecting structure located withinsaid array and between at least a pair of said light detection means forforming mirror images of said pair of light detection means, therebyfurther increasing the apparent number of light detection means whoseindividual polar light response characteristics overlap in the plane ofsaid source, the exterior surfaces of said wedge-shaped structure beinglight reflective to form said mirror images.

8. Light collection and detection apparatus which exhibits asubstantially uniform response characteristic with respect to a diffusespot of light which may emanate from any point on a planar source,comprising:

a plurality of photomultipliers, each having a known polar lightresponse characteristic which is nonuniform with respect to at leastsome of the possible points from which said diffuse spot of light mayemanate on said source, each of said photomultipliers for developing anoutput signal representative of the intensity of said diffuse spot oflight, said photomultipliers being arranged in a predetermined array ina plane substantially parallel to that of said source and separatedtherefrom by a chosen distance to effect an overlapping of saidindividual light response characteristics by a selected amount in theplane of said source;

light-reflecting means, arranged adjacent to at least some of saidphotomultipliers, for forming mirror images of at least some of saidphotomultipliers, thereby increasing the apparent number ofphotomultipliers in said array whose individual polar light responsecharacteristics overlap in the plane of said source;

and means for additively combining the output signals of saidphotomultipliers to develop a resultant output signal whose amplitude issubstantially linearly proportional to the intensity of said diffusespot of light, regardless of the location of the point on said sourcefrom which said diffuse spot of light emanates.

9. Apparatus constructed in accordance with claim 8 wherein saidlight-reflecting means is a boxlike structure, having wallssubstantially perpendicular to the plane of said source and surroundingsaid array of light detection means, the interior surfaces of saidstructure being light-reflective to form said mirror images.

10. Apparatus constructed in accordance with claim 8 wherein saidlight-reflecting means comprises at least one wedge-shapedlight-reflecting structure located within said array and between atleast a pair of said light detection means for forming mirror images ofsaid pair of light detection means, the exterior surfaces of saidwedge-shaped structure being light-reflective to form said mirrorimages.

11. Light collection and detection apparatus, useful in conjunction withan electro-optical system which scans an image plane with a spot oflight such that the spot may occur at any point in said image plane,comprising:

planar light-diffusing means located adjacent and substantially parallelto said image plane, for diffusing the spot of light occurring in saidimage plane to provide a diffuse spot of light which may emanate fromany point on a planar source represented by said diffusing means;

a plurality of light detection means, each having a known polar lightresponse characteristic which is nonuniform with respect to at leastsome of the possible points from which said diffuse spot of light mayemanate on said diffusing means, each of said detection means fordeveloping an output signal representative of the intensity of saiddiffuse spot of light, said detection means being arranged in apredetermined array to effect an overlapping of said individual lightresponse characteristics by a selected amount in the plane of saiddiffusing means;

and means for combining the output signals of said light detection meansto develop a resultant output signal whose amplitude is substantiallylinearly proportional to the intensity of said diffuse spot of lightregardless of the location of the point on said diffusing means fromwhich said spot of diffuse light emanates.

12. Light collection and detection apparatus constructed in accordancewith claim 11 wherein said planar light-diffusing means comprises a thinglass plate having a translucent, white,

opal surface, with said opal surface located adjacent said image plane.

13. Apparatus constructed in accordance with claim 11 wherein said lightdetection means are arranged in said predetermined array in a planesubstantially parallel to that of said source and separated therefrom bya chosen distance, thereby to effect said selected amount of overlappingof said light response characteristics.

14. Apparatus constructed in accordance with claim 11 wherein saidapparatus additionally includes light-reflecting means, arrangedadjacent to at least some of the light detection means in said array,for forming mirror images of at least some of said light detectionmeans, thereby increasing the apparent number of light-detection meansin said array whose individual polar light response characteristicsoverlap in the plane of said source.

15. Apparatus constructed in accordance with claim 14 wherein saidlight-reflecting means is a boxlike structure, having wallssubstantially perpendicular to the plane of said source and surroundingsaid array of light detection means, the interior surfaces of saidstructure being light reflective to form said mirror images.

16 Apparatus constructed in accordance with claim 14 wherein saidlight-reflecting means comprises at least one wedge-shapedlight-reflecting structure located within said array and between atleast a pair of said light detection means for forming mirror images ofsaid'pair of light detection means, the exterior surfaces ofsaidIwedge-shaped structure being light-reflective to form said mirforimages.

17. Apparatus constructed in accordance with claim 11 wherein saidapparatus additionally includes a boxlike lightreflecting structure,having walls substantially perpendicular to the plane of said source andsurrounding said array of light detection means, for forming mirrorimages at least some of said light detection means, thereby increasingthe apparent number of light detection means whose individual polarlight response characteristics overlap in the plane of said source, theinterior surfaces of said boxlike structure being lightreflective toform said mirror images;

and at least one wedge-shaped light-reflecting structure located withinsaid array and between at least a pair of said light detection means forforming mirror images of said pair of light detection means, therebyfurther increasing the apparent number of light detection means whoseindividual polar light response characteristics overlap in the plane ofsaid source, the exterior surfaces of said wedge-shaped structure beinglight-reflective to form said mirror images.

10 18. Light collection and detection apparatus, useful in conjunctionwith an electro-optical system which scans an image plane with a spot oflight such that the spot may occur at any point in said plane,comprising:

a thin, substantially flat plate of glass having a translucent, white,opal surface located adjacent said image plane, for diffusing the spotof light occuring in said image plane to provide a diffuse spot of lightwhich may emanate from any point on the planar source represented by theopal surface of said glass plate;

a plurality of photomultipliers, each having a known polar lightresponse characteristic which is nonuniform with respect to at leastsome of the possible points from which said diffuse spot of light mayemanate on said opal surface, each of said photomultipliers fordeveloping an output signal representative of the intensity of saiddiffuse spot of light, said photomultipliers being arranged in apredetermined array in a plane substantially parallel to that of saidopal surface and separated therefrom by a chosen distance, to effect anoverlapping of said individual light response characteristics by aselected amount in the plane of said opal surface;

light-reflecting means, arranged adjacent to at least some of saidphotomultipliers, for forming mirror images of at least some of saidphotomultipliers, thereby increasing the apparent number ofphotomultipliers in said array whose individual polar light responsecharacteristics overlap in the plane of said opal surface;

and means for additively combining the output signals of saidphotomultipliers to develop a resultant output signal whose amplitude issubstantially linearly proportional to the intensity of said diffusespot of light, regardless of the location of the point on said opalsurface from which said spot of diffuse light emanates.

19. Apparatus constructed in accordance with claim 18 wherein saidlight-reflecting means is a boxlike structure, having wallssubstantially perpendicular to the plane of said source and surroundingsaid array of light detection means, the interior surfaces of saidstructure being light-reflective to form said mirror images,

20. Apparatus constructed in accordance with claim 18 wherein saidlight-reflecting means comprises at least one wedge-shapedlight-reflecting structure located within said array and between atleast a pair of said light detection means for forming mirror images ofsaid pair of light detection means, the exterior surfaces of saidwedge-shaped structure being lightreflective to form said mirror images.

1. Light collection and detection apparatus which exhibits asubstantially uniform response characteristic with respect to anintensity-modulated diffuse spot of light which may emanate from anypoint on a planar source, comprising: a plurality of light detectionmeans, each having a known polar light response characteristic which isnonuniform with respect to at least some of the possible points fromwhich said intensity-modulated diffuse spot of light may emanate on saidsource, each of said detection means for developing an output signalrepresentative of the intensity of said diffuse spot of light, saidplurality of detection means being arranged in a predetermined array toeffect an overlapping of said individual light response characteristicsby a selected amount in the plane of said source; and means forcombining the output signals of said light detection means to develop aresultant output signal whose amplitude is substantially linearlyproportional to the intensity of said diffuse spot of light regardlessof the location of the point on said source from which said spot oflight emanates.
 2. Apparatus constructed in accordance with claim 1wherein said light detection means are arranged in said predeterminedarray in a plane substantially parallel to that of said source ansseparated therefrom by a chosen distance, thereby to effect saidselected amount of overlapping of said light response characteristics.3. Apparatus constructed in accordance with claim 1 wherein each of saidlight detection means is a photomultiplier and wherein said means forcombining the output signals of said photomultipliers is a conductorconnected to the output of each photomultiplier.
 4. Apparatusconstructed in accordance with claim 1 wherein said apparatusadditionally includes light-reflecting means, arranged adjacent to atleast some of the light-detection means in said array, for formingmirror images of at least some of said light detection means, therebyincreasing the apparent number of light detection means in said arraywhose individual polar light response characteristics overlap in theplane of said source.
 5. Apparatus constructed in accordance with claim4 wherein said light-reflecting means is a boxlike structure, havingwalls substantially perpendicular to the plane of said source andsurrounding said array of light detection means, the interior surfacesof said structure being light-reflective to form said mirror images. 6.Apparatus constructed in accordance with claim 4 wherein saidlight-reflecting means comprises at least one wedge-shapedlight-reflecting structure located within said array and between atleast a pair of said light detection means for forming mirror images ofsaid pair of light detection means, the exterior surfaces of saidwedge-shaped structure being light reflective to form said mirrorimages.
 7. Apparatus constructed in accordance with claim 1 wherein saidapparatus additionally includes a boxlike light-reflecting structure,having walls substantially perpendicular to the plane of said source andsurrounding said array of light detection means, for forming mirrorimages of at least some of said light detection means, therebyincreasing the apparent number of light detection means whose individualpolar light response characteristics overlap in the plane of saidsource, the interior surfaces of said boxlike structure beinglight-reflective to form said mirror images; and at least onewedge-shaped light reflecting structure located within said array andbetween at least a pair of said light detection means for forming mirrorimages of said pair of light detection means, thereby further increasingthe apparent number of light detection means whose individual polarlight response characteristics overlap in the plane of said source, theexterior surfaces of said wedge-shaped structure being light reflectiveto form said mirror images.
 8. Light collection and detection apparatuswhich exhibits a substantially uniform response characteristic withrespect to a diffuse spot of light which may emanate from any point on aplanar source, comprising: a plurality of photomultipliers, each havinga known polar light response characteristic which is nonuniform withrespect to at least some of the possible points from which said diffusespot of light may emanate on said source, each of said photomultipliersfor developing an output signal representative of the intensity of saiddiffuse spot of light, said photomultipliers being arranged in apredetermined array in a plane substantially parallel to that of saidsource and separated therefrom by a chosen distance to effect anoverlapping of said individual light response characteristics by aselected amount in the plane of said source; light-reflecting means,arranged adjacent to at least some of said photomultipliers, for formingmirror images of at least some of said photomultipliers, therebyincreasing the apparent number of photomultipliers in said array whoseindividual polar light response characteristics overlap in the plane ofsaid source; and means for additively combining the output signals ofsaid photomultipliers to develop a resultant output signal whoseamplitude is substantially linearly proportional to the intensity ofsaid diffuse spot of light, regardless of the location of the point onsaid source from which said diffuse spot of light emanates.
 9. Apparatusconstructed in accordance with claim 8 wherein said light-reflectingmeans is a boxlike structure, having walls substantially perpendicularto the plane of said source and surrounding said array of lightdetection means, the interior surfaces of said structure beinglight-reflective to form said mirror images.
 10. Apparatus constructedin accordance with claim 8 wherein said light-reflecting means comprisesat least one wedge-shaped light-reflecting structure located within saidarray and between at least a pair of said light detection means forforming mirror images of said pair of light detection means, theexterior surfaces of said wedge-shaped structure being light-reflectiveto form said mirror images.
 11. Light collection and detectionapparatus, useful in conjunction with an electro-optical system whichscans an image plane with a spot of light such that the spot may occurat any point in said image plane, comprising: planar light-diffusingmeans located adjacent and substantially parallel to said image plane,for diffusing the spot of light occurring in said image plane to providea diffuse spot of light which may emanate from any point on a planarsource represented by said diffusing means; a plurality of lightdetection means, each having a known polar light response characteristicwhich is nonuniform with respect to at least some of the possible pointsfrom which said diffuse spot of light may emanate on said diffusingmeans, each of said detection means for developing an output signalrepresentative of the intensity of said diffuse spot of light, saiddetection means being arranged in a predetermined array to effect anoverlapping of said individual light response characteristics by aselected amount in the plane of said diffusing means; and means forcombining the output signals of said light detection means to develop aresultant output signal whose amplitude is substantially linearlyproportional to the intensity of said diffuse spot of light regardlessof the location of the point on said diffusing means from which saidspot of diffuse light emanates.
 12. Light collection and detectionapparatus constructed in accordance with claim 11 wherein said planarlight-diffusing means comprises a thin glass plate having a translucent,wHite, opal surface, with said opal surface located adjacent said imageplane.
 13. Apparatus constructed in accordance with claim 11 whereinsaid light detection means are arranged in said predetermined array in aplane substantially parallel to that of said source and separatedtherefrom by a chosen distance, thereby to effect said selected amountof overlapping of said light response characteristics.
 14. Apparatusconstructed in accordance with claim 11 wherein said apparatusadditionally includes light-reflecting means, arranged adjacent to atleast some of the light detection means in said array, for formingmirror images of at least some of said light detection means, therebyincreasing the apparent number of light-detection means in said arraywhose individual polar light response characteristics overlap in theplane of said source.
 15. Apparatus constructed in accordance with claim14 wherein said light-reflecting means is a boxlike structure, havingwalls substantially perpendicular to the plane of said source andsurrounding said array of light detection means, the interior surfacesof said structure being light reflective to form said mirror images. 16Apparatus constructed in accordance with claim 14 wherein saidlight-reflecting means comprises at least one wedge-shapedlight-reflecting structure located within said array and between atleast a pair of said light detection means for forming mirror images ofsaid pair of light detection means, the exterior surfaces of saidwedge-shaped structure being light-reflective to form said mirrorimages.
 17. Apparatus constructed in accordance with claim 11 whereinsaid apparatus additionally includes a boxlike light-reflectingstructure, having walls substantially perpendicular to the plane of saidsource and surrounding said array of light detection means, for formingmirror images at least some of said light detection means, therebyincreasing the apparent number of light detection means whose individualpolar light response characteristics overlap in the plane of saidsource, the interior surfaces of said boxlike structure beinglight-reflective to form said mirror images; and at least onewedge-shaped light-reflecting structure located within said array andbetween at least a pair of said light detection means for forming mirrorimages of said pair of light detection means, thereby further increasingthe apparent number of light detection means whose individual polarlight response characteristics overlap in the plane of said source, theexterior surfaces of said wedge-shaped structure being light-reflectiveto form said mirror images.
 18. Light collection and detectionapparatus, useful in conjunction with an electro-optical system whichscans an image plane with a spot of light such that the spot may occurat any point in said plane, comprising: a thin, substantially flat plateof glass having a translucent, white, opal surface located adjacent saidimage plane, for diffusing the spot of light occuring in said imageplane to provide a diffuse spot of light which may emanate from anypoint on the planar source represented by the opal surface of said glassplate; a plurality of photomultipliers, each having a known polar lightresponse characteristic which is nonuniform with respect to at leastsome of the possible points from which said diffuse spot of light mayemanate on said opal surface, each of said photomultipliers fordeveloping an output signal representative of the intensity of saiddiffuse spot of light, said photomultipliers being arranged in apredetermined array in a plane substantially parallel to that of saidopal surface and separated therefrom by a chosen distance, to effect anoverlapping of said individual light response characteristics by aselected amount in the plane of said opal surface; light-reflectingmeans, arranged adjacent to at least some of said photomultipliers, forforming mirror images of at least some of said photomultipliers, therebyincreasing The apparent number of photomultipliers in said array whoseindividual polar light response characteristics overlap in the plane ofsaid opal surface; and means for additively combining the output signalsof said photomultipliers to develop a resultant output signal whoseamplitude is substantially linearly proportional to the intensity ofsaid diffuse spot of light, regardless of the location of the point onsaid opal surface from which said spot of diffuse light emanates. 19.Apparatus constructed in accordance with claim 18 wherein saidlight-reflecting means is a boxlike structure, having wallssubstantially perpendicular to the plane of said source and surroundingsaid array of light detection means, the interior surfaces of saidstructure being light-reflective to form said mirror images. 20.Apparatus constructed in accordance with claim 18 wherein saidlight-reflecting means comprises at least one wedge-shapedlight-reflecting structure located within said array and between atleast a pair of said light detection means for forming mirror images ofsaid pair of light detection means, the exterior surfaces of saidwedge-shaped structure being light-reflective to form said mirrorimages.